Considerable progress has been made in the last several years in increasing the yield of sugarcane by improving the varieties being planted, enriching the soil with fertilizers and irrigating the soil in climates which do not naturally provide sufficient moisture for optimum plant growth. More recent efforts in improving sugar production have increasingly turned toward the use of chemicals in modifying the controlling of the physiological processes of sugarcane, particularly in ripening prior to harvest. See U.S. Pat. Nos. 3,244,865; 3,245,775; 3,291,592; 3,482,959; 3,482,961; 3,493,361; 3,505,056; 3,660,072 and 3,671,219.
With some compounds previously suggested for this purpose, there has been some concern about their resistance to breakdown in the plant and their persistence in the soil when the intended use of the sugar is nutritive as opposed to industrial (e.g., in fermentation processes). Consequently, extensive efforts continue to be made in searching for effective chemical agents that can be used to modify the ripening of sugarcane so as to increase the sucrose yield therefrom.
Certain polysubstituted benzoic acid compounds, for example, the dimethylamine salt of 2,3,6-trichlorobenzoic acid and alkyl esters of 2-methoxy-3,6-dichlorobenzoic acid, have been found to be effective sugarcane ripening agents. The dimethylamine salt of 2,3,6-trichlorobenzoic acid compound, however, not only has high hormonal and herbicidal activity on many plants, it also tends to possess an unacceptable stability which may result in a residue in the treated crop at a level greater than that which may be established as the maximum allowable. See, for example, "Sugarcane Ripening with Chemicals", Nickett et al., 1967 Reports, Hawaiian Sugar Technologists, pp. 104 to 109 at page 105. The alkyl esters of 2-methoxy-3,6 dichlorobenzoic acid compounds possess high volatility, relatively high ultraviolet instability, and poor reproducibility of results in field use.
Generally speaking, chemicals selected for evaluation have been of types which have been previously found active in work with other plants as plant hormones, herbicides or inhibitors of growth of terminal buds, or active in killing the spindle or cane upon topical micro-application, etc. However, among the compounds heretofore found to be useful for such other special purposes, surprisingly few have been found effective in controlling the ripening of sugarcane in the desirable manner. No predictable relationship has been recognized to date between (a) the chemical structure of such compounds, (b) their phytotoxic effects, or (c) their physiological effects on the morphogenetic development of the plant, and their activity in having positive effects on ripening. In other words, the effectiveness of a compound in controlling the ripening of sugarcane and thereby increasing sugar yield remains essentially unpredictable, and the search for suitable agents continues to be fundamentally empirical.